Photographic element comprising a gelatin aqueous composition containing a halomethyl ketone of benzyloxycarbonyl phenylalanine

ABSTRACT

AQUEOUS SOLUTIONS OF GELATIN AND GELATIN-CONTAINING LAYERS SUCH AS PHOTOGRAPHIC SILVER HALIDE EMULSIONS CONTAINING BENZLOXYCARBONYL PHENYLALNINE CHLOROMETHYL KETONE AND BENZYLOXYCARBONYL PHENYLALANINE BROMOMETHYL KETONE TO CONTROL ENZYME ACTIVITY AND DECELERATE BACTERIAL GROWTH AND REPRODUCTION. A PHENOLIC BIOSTAT MAY OPTIONALLY BE ADDED FOR IMPROVED RESULTS.

United States Patent Ofice PHOTOGRAPHIC ELEMENT COMPRISING A GELATIN AQUEOUS COMPOSITION CON- TAINING A HALOMETHYL KETONE OF BENZYLOXYCARBONYL PHENYLALANINE Elliott N. Shaw, Shoreham, N.Y., assiguor to Polaroid Corporation, Cambridge, Mass. No Drawing. Filed May 22, 1972, Ser. No. 255,709 Int. Cl. G03c 1/02; A231 3/34 US. CI. 96-94 R 7 Claims ABSTRACT OF THE DISCLOSURE Aqueous solutions of gelatin and gelatin-containing layers such as photographic silver halide emulsions containing benzyloxycarbonyl phenylalanine chloromethyl ketone and benzyloxycarbonyl phenylalanine bromomethyl ketone to control enzyme activity and decelerate bacterial growth and reproduction. A phenolic biostat may optionally be added for improved results.

BACKGROUND OF THE INVENTION This invention relates to controlling enzyme activity and thereby decelerating bacterial growth and reproduction in gelatin and to compositions employing gelatin. Another aspect of the invention relates to silver halide emulsions and photographic elements in which enzyme activity and continued bacterial growth and reproduction is controlled.

DESCRIPTION OF THE PRIOR ART Photographic gelatin is a chemically stable substance when stored in a warm aqueous emulsion under aseptic conditions. However, an aqueous gelatin emulsion which is contaminated with pathogenic bacteria is rapidly degraded by what is known as bacterial action. In such bacterial action gelatin is not directly consumed by the bacteria because of the large size of gelatins polypeptide molecules. Instead, the bacteria generate and inoculate gelatin also changes its viscosity and seriously interferes with the anchoring characteristics of thin subbing layers.

It has been generally accepted that gelatin sols and photographic emulsions held for extended periods in cold storage before coating require not only a depressant for slowing down the living processes of organisms, but also a mechanism for destroying or inactivating the proteolytic enzymes already present or being produced by the still viable organisms. If the enzymes are not destroyed or inactivated, they will hydrolyze the gelatin sol and produce the other above-mentioned deleterious results.

Unfortunately, most of the more frequently used emulsion biostats at practical concentrations are apt to act more as an enzyme preservative than a depressant. Thus, although bacterial activity is slowed, a minute quantity of enzyme already formed remains active. Pasteurization at 170 -180 F. destroys much of the enzyme potential but recontamination does occur and there are systems where pasteurization is inconvenient or impractical.

Some of the compounds useful as gelatin preservatives in the past have been 1,3-diketones including highly 3 ,778,276 Patented Dec. 11, 1973 enolized 1,3-diketones such as acetyl acetone; formaldehyde, phenol, thymol, esters of p-hydroxybenzoic acid, alcohols, and others as described in US. Pat. 2,226,183 of Stand et al., issued Dec. 24, 1940; British Pat. 987,010 of Du Pont issued Mar. 24, 1965; and British Pat. 968,883 of Gevaert issued Sept. 2, 1964. These compounds, however, are directed towards slowing down the living processes of organisms and do very little in inactivating the proteolytic enzymes already present.

There are compounds known to be enzyme inhibitors such as iodoacetic acid and various fluorides such as sodium fluoride, potassium fluoride and potassium fluosilicate, but in permissible concentrations their activity was found to be low in certain gel sols and photographic emulsions and under some conditions they fail entirely, but they do not all function in an equivalent manner when incorporated into a gelatin composition.

US. Pat. No. 3,503,746 discloses and claims the employment of L-l-tosylamino-2-phenethyl-chloromethylketone (TPCK) in gelatin solutions to control enzyme growth in gelatin solutions. However, the eflfectiveness at given concentrations of TPCK in gelatin composition leaves something to be desired.

SUMMARY OF THE INVENTION It has now been found that benzyloxycarbonyl phenylalanine chloromethyl ketone (ZIPCK) and benzyloxycarbonyl phenylalanine bromomethyl ketone (ZPBK) are highly effective in inhibiting the action of enzymes in an aqueous gelatin solution. ZPCK and ZPBK can be incorporated into gelatino-silver halide emulsions, gelatin interlayers and gelatin overcoats and will control enzyme activity, thus inhibiting the degradation of gelatin and the attendant bacterial growth. The enzyme growth inhibition is accomplished without any adverse eifect on the photographic utility of the gelatin composition. A phenolic biostat may also be employed with the enzyme growth inhibitor.

DETAILED DESCRIPTION OF THE INVENTION ZPCK and ZPBK, halo methyl ketones of benzyloxycarbonyl phenylalanine, have been found to be highly effective in inhibiting enzyme action in gelatin compositions which results in the degradation of the gelatin and obviates its fitness for employment in, for example, photographic film units, particularly photographic silver halide emulsions. The employment of ZPCK and ZPBK has been found to provide superior and unexpected results compared to conventional enzyme inhibitors for gelatin compositions. For example, compared to TPCK, referred to above, ZPCK and ZPBK show an eflectiveness, in terms of rate of enzyme inactivation, of as much as times greater. In addition, ZPCK and ZPBK are eflective against enzymes resistant to the action of TPCK.

ZPCK and ZPBK may be employed satisfactorily over a relatively wide range. Preferably, the compounds are employed at a range of 25 to 300 ppm. per gram of gelatin, more preferably 40 ppm. ZPCK and ZPBK are introduced into the gelatin composition in suitable organic solvents, e.g., methanol or dimethyl sulfoxide.

ZPCK and ZPBK are known compounds and the methods of preparation may be found, for example, in Methods in Enzymology (C. H. W. Hirs, ed.), p. 684, vol. XI, Academic Press, New York (1967) and J. Biol-Chem. 243, 6312 (1968).

The following non-limiting examples illustrate the preparation of ZPCK and ZPBK.

Example I A cold solution of carbobenzoxy phenylalanine acid chloride freshly prepared from 3.25 g. of carbobenzoxy- L-phenylalanine and 2.39 g. of phosphorous pentachloride was added to the cold solution of diazo methane prepared according to the procedure set forth on page 250 of Org. Syn., volume 4. After stirring the solution for 20 minutes, a mixture of 16 milliliters of 32% hydrogen bromide in acetic acid, 22 milliliters of 48% hydrogen bromide and 4.4 milliliters of Water were added and the mixture shaken vigorously. The ether layer was separated, washed with water, dried over anhydrous sodium sulphate and then evaporated under a vacuum to a solid. The solid was re crystallized from ethanol to give 2 g. of white needles having a melting point of 97-99 C. of

benzyloxy carbonyl phenylalanine bromomethyl ketone.

Example II A cold diazo methane solution was added rapidly to a cold solution of carbobenzoxy phenylalanine acid chloride freshly prepared from 6.8 g. of caubobenzoxy-L- phenylalanine and 5.64 moles of phosphorus pentachloride in 150 milliliters of diethyl ether. The reaction mixture was then stirred for 20 minutes at C. To the mixture was then added 32 milliliters concentrated hydrochloric acid and milliliters of water and stirring was continued for an additional 30 minutes. The ether layer was then separated, washed with water and dilute sodium carbonate solution. The solution was then dried over anhydrous sodium sulphate, filtered and evaporated under a vacuum to an oil. The oil was recrystallized from 200 milliliters of ethanol and water (1:1 ratio) to give 2 g. of white needles melting at 99-102 C. of:

benzyloxy carbonyl phenylalanine chloromethyl ketone.

Conventional biostats, such as the phenolic biostats, e.g., phenol, thymol, p-chloro-meta-xylenol, and the like, may also be employed in combination with the enzyme inhibitors of the present invention in order to obtain the combined effect of bacterial control to prevent enzyme production and the inhibition of enzyme attack on the gelatin.

The following non-limiting examples illustrate the employment of the enzyme inhibitors of the present invention.

Table 1 illustrates the effectiveness of the enzyme inhibitors of the present invention, as evaluated by the degree of viscosity change of gelatin silver halide emulsions. Viscosity is measured in seconds at 40 C. using an Ubbelohde tube.

The above table indicates that substantially no viscosity change occurs employing the enzyme inhibitors of the present invention.

The following experiment was designed to illustrate the inhibiting action of ZPCK and ZPBK on an emulsion that has been innoculated with a bad emulsion, i.e., one in which liquefaction and instability have been noted visually. The ratio of bad to good was 1/ 8 by weigh-t.

TABLE 2 Beginning signs of liquefaction TPCK (500 p.p.m./g. gel, 5% gel emul After 15 days.

sion). ZPBK (500 p.p.m./g. gel, 5% gel emul- After 35 days. sion). ZPBK (500 p.p.m./g. gel, 10% gel emul- After 38 days.

sion).

ZPCK (500 p.p.m./g. gel, 5% gel emul- Do.

sion). ZPCK (500 p.p.m./g. gel, 10% gel emul- After 42 days.

sion). Control (5% gel emulsion) After 3 days. Control (10% gel emulsion) After 5 days.

I invention may be employed in any aqueous gelatin composition, but are particularly useful in gelatin-containing photographic elements, such as silver halide emulsions, dye image-forming material-containing layers, interlayers, and overcoats, including filter layers, spacer layers, and antihalation layers.

Emulsions employing the enzyme inhibitors of the present invention may be prepared by conventional methods and may include various adjuncts, for example, chemical sensitizing agents of U.S. Pats. Nos. 1,574,944; 1,623,499; 2,410,689; 2,597,856; 2,597,915; 2,487,850; 2,518,698; 2,521,926; and the like; all according to the traditional procedures of the art, as described in Neblette, C. B., photography, Its Materials and Processes, 6th ed., 1962.

Optical sensitization of the emulsions silver halide crystals may be accomplished by contact of the emulsion composition with an effective concentration of the selected optical sensitizing dyes dissolved in an appropriate dispersing solvent such as methanol, ethanol, acetone, water, and the like; all according to the traditional procedures of the art, as described in Hammer, F. M., The Cyanine Dyes and Related Compounds.

Additional optional additives, such as coating aids, hardeners, viscosity-increasing agents, stabilizers, preservatives, and the like, for example, those set forth hereinafter, also may be incorporated in the emulsion formulation, according to the conventional procedures known in the photographic emulsion manufacturing art.

The photoresponsive material of the photographic emulsion will, as previously described, preferably comprise a crystal of silver, for example, one or more of the silver halides such as silver chloride, silver iodide, silver bromide, or mixed silver halides such as silver chlorobromide, silver chloroiodobromide or silver iodobromide, of varying halide ratios and varying silver concentrations.

As a binder for the respective emulsion strata, the aforementioned gelatin may be replaced in part with some other colloidal material such as albumin; casein; or zein; or resins such as a cellulose derivative, as described in U.S. Pats. Nos. 2,322,085 and 2,327,808; polyacrylamides, as described in U.S. Pat. No. 2,541,474; and vinyl polymers such as those described in an extensive multiplicity of readily available U.S. and foreign patents.

Photographic emulsions containing the enzyme inhibitor of the invention can also contain speed-increasing compounds such as quaternary ammonium compounds,

polyethylene glycols or thioethers. Frequently, useful effects can be obtained by adding the aforementioned speed-increasing compounds to the photographic developer solutions instead of, or in addition to, the photographic emulsions.

Photographic elements containing the enzyme inhibitor of the instant invention can be used in various kinds of photographic systems. In addition to being useful in X-ray and other non-optically sensitized systems, they can also be used in orthochromatic, panchromatic, and infrared sensitive systems. The sensitizing addenda can be added to photographic systems before or after any sensitizing dyes which are used.

Gelatin layers containing the inhibitor of the present invention may also be used in color photography, for example, in the color processes disclosed in US. Pat. No. 2,983,606, where the enzyme inhibitor, in addition to being employed in the silver halide emulsion, is also disposed in the interlayers, including gelatin layers containing the dye developers. The inhibitor is also useful in layers containing other dye image-forming materials such as those disclosed in US. Pats. Nos. 2,647,049; 2,661,293; 2,698,244; 2,698,798; 2,802,735; 3,148,062; 3,227,550; 3,227,551; 3,227,552; 3,277,554; 3,243,294; 3,330,655; 3,347,671; 3,352,672; 3,364,022; 3,443,939; 3,443,940; 3 443,941; 3,443,943; 2,774,668; and 3,087,817.

Silver halide emulsions containing the enzyme inhibitor of the invention can be used in diffusion transfer processes which utilize the undeveloped silver halide in non-image areas of the negative to form a positive by dissolving the undeveloped silver halide and precipitating it on a silver layer in close proximity to the original silver halide emulsion layer. Such processes are described in US.

6 Pats. Nos. 2,543,181 issued Feb. 27, 1951 and 2,662,822 issued Dec. 15, 1953.

What is claimed is:

1. A photographic element which includes an aqueous gelatin composition containing, as an enzyme inhibitor, a halomethyl ketone of benzyloxycarbonyl phenylalanine.

2. A product as defined in claim 1 wherein said composition is a silver halide emulsion.

3. A product as defined in claim 1 wherein said composition is a dye image-forming material containing layer.

4. The product as defined in claim 3 wherein said dye image-forming material is a dye developer.

5. The product as defined in claim 1 wherein said inhibitor is benzyloxycarbonyl phenylalanine chloromethyl ketone.

6. The product as defined in claim 1 wherein said inhibitor is benzyloxycarbonyl phenylalanine bromomethyl ketone.

7. The product as defined in claim 1 which includes a phenolic biostat.

References Cited UNITED STATES PATENTS 3/1970 McClintock 96-94 R US. Cl. X.R. 

